This invention relates generally to the treatment of gases and, more particularly, to the treatment, such as by chemical cooling, of gases such as those produced or generated for inflation of inflatable devices such as airbag cushions.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as "an inflator."
While many types of inflator devices have been disclosed in the art for use in the inflating of one or more inflatable restraint system airbag cushions, inflator devices which rely on the combustion of a pyrotechnic, fuel and oxidizer combination or other form of gas generant to produce or at least in part form the inflation gas issuing forth therefrom have been commonly employed in conjunction with vehicular inflatable restraint airbag cushions.
Usually, the combustion processing occurring in such inflator devices has associated therewith the generation or production of significant quantities of heat. As will be appreciated, it may be desired or preferred to generally limit the temperature of the inflation gas and which gas may, intentionally or inadvertently, exit from the associated inflatable device, such as either during or subsequent to the inflation thereof.
In general, the ability to design airbag inflator devices to cool the generated gases to any particularly selected temperature has been rather limited. For example, it is relatively common for modern airbag inflator devices to incorporate a form of mechanical cooling means such as through the conduction of heat into a heat sink, which typically has high thermal conductivity as well as large surface area and mass with which to absorb heat. In particular, it is common for modem inflator devices to include an internal screen pack such as to cool the generated gas and to filter or otherwise remove solid residue remaining from the combustion process. Consequently, the final temperature of the gas from such a device is typically dependent on the gas temperature of the combustion process, the heat transfer to the inflator housing and associated screen or filter materials and the gas expansion into the associated airbag cushion.
Many factors may serve or act to control or limit the amount of cooling which may be realized through the use of such mechanical cooling means. For example, the amount of cooling realizable through such use of a mechanical cooling means will typically be limited by factors such as the length of time the generated gas is in contact with the cooling media as well as the physical properties or parameters, such as mass, surface area, melt temperature and thermal conductivity of the cooling media.
At the present time, sodium azide is a commonly accepted and used gas generating material. While the use of sodium azide meets current industry specifications, guidelines and standards, such use may involve or raise potential handling, supply and disposal concerns. As a result, the development and use of other suitable gas generant materials has been pursued. Thus, efforts have been directed to the development of azide-free pyrotechnics for use in such inflator device applications.
At least certain of such azide-free pyrotechnic materials burn at significantly higher temperature than conventional azide-based pyrotechnics. For example, whereas commonly-used airbag inflator device azide pyrotechnics form gaseous products in a temperature range of about 1400 K to about 1500 K, the gaseous products associated with such azide-free pyrotechnics may more typically be formed at a temperature of about 1700 K to about 2500 K and, more commonly, at a temperature of about 1700 K to about 1900 K. In fact, the higher temperatures associated with such azide-free pyrotechnics are often at or above the melt temperature of many of the mechanical cooling media materials commonly associated with current airbag inflator devices. Consequently, the further development and use of more efficient pyrotechnics, such as at least certain azide-free pyrotechnics, has been somewhat limited or hampered by limitations in the abilities of conventional inflator devices and common mechanical cooling media materials to accept such higher combustion temperatures.
Thus, there is a need and a demand for assemblies and processing techniques which can provide an alternative to such mechanical cooling of gases and such as may more easily be adapted for use in conjunction with the cooling of higher temperature gases.
In the past, certain inflator devices have used or attempted to use a form of chemical coolant either alone or in conjunction with mechanical cooling of generated gases. Such chemical cooling has typically relied on the use of one or more endothermically reactable chemical coolant materials with which hot generated gases come into contact such that the hot generated gases are cooled.
A significant limitation to the more effective and increased use of such endothermically reactable chemical coolants has been that such coolants tend to experience significant shrinkage or reduction in size upon reaction. In practice, such shrinkage or size reduction may amount to a total reduction of 50 percent or more. As a result of experiencing such size reduction, a body of such a chemical coolant such as contained within an inflator device may undesirably form channels or other form of passageways therethrough which may serve to limit and minimize contact between the hot gases and the chemical coolant and thus reduce or limit the effective of the chemical coolant.
Thus, there is a need and a demand for assemblies and processing techniques which can permit either or both the more widespread or efficient use of such chemical coolants such as by minimizing or avoiding the possibly detrimental effects of size reduction or gas passage channel formation such as associated with the use of a body of such a chemical coolant.